Using Postgres Enum Types in Ent Schema

Using Postgres Enum Types in Ent Schema

Enum types are data structures that consist of a predefined, ordered set of values. By default, when using field.Enum in your Ent schema, Ent uses simple string types to represent the enum values in PostgreSQL and SQLite. However, in some cases, you may want to use the native enum types provided by the database.

This guide explains how to define a schema field that uses a native PostgreSQL enum type and configure the schema migration to manage both Postgres enums and the Ent schema as a single migration unit using Atlas.

Atlas Pro Feature

atlas login

Install Atlas

To install the latest release of Atlas, simply run one of the following commands in your terminal, or check out the Atlas website:

macOS + Linux
Homebrew
Docker
Windows

curl -sSf https://atlasgo.sh | sh

brew install ariga/tap/atlas

docker pull arigaio/atlas
docker run --rm arigaio/atlas --help

If the container needs access to the host network or a local directory, use the --net=host flag and mount the desired directory:

docker run --rm --net=host \
  -v $(pwd)/migrations:/migrations \
  arigaio/atlas migrate apply
  --url "mysql://root:pass@:3306/test"

Download the latest release and move the atlas binary to a file location on your system PATH.

$ atlas login a8m
You are now connected to "a8m" on Atlas Cloud.

Composite Schema

An ent/schema package is mostly used for defining Ent types (objects), their fields, edges and logic. External enum types, or any other database objects do not have representation in Ent models - A Postgres enum type can be defined once in your Postgres schema, and may be used multiple times in different fields and models.

In order to extend our PostgreSQL schema to include both custom enum types and our Ent types, we configure Atlas to read the state of the schema from a Composite Schema data source. Follow the steps below to configure this for your project:

Create a schema.sql that defines the necessary enum type there. In the same way, you can define the enum type in Atlas Schema HCL language:

Using SQL
Using HCL

schema.sql

CREATE TYPE status AS ENUM ('active', 'inactive', 'pending');

schema.hcl

schema "public" {}
enum "status" {
  schema = schema.public
  values = ["active", "inactive", "pending"]
}

In your Ent schema, define an enum field that uses the underlying Postgres ENUM type:

ent/schema/user.go

// Fields of the User.
func (User) Fields() []ent.Field {
    return []ent.Field{
        field.Enum("status").
            Values("active", "inactive", "pending").
            SchemaType(map[string]string{
                dialect.Postgres: "status",
            }),
    }
}

note

In case a schema with custom driver-specific types is used with other databases, Ent falls back to the default type used by the driver (e.g., TEXT in SQLite and ENUM (...) in MariaDB or MySQL)s.

Create a simple atlas.hcl config file with a composite_schema that includes both your custom enum types defined in schema.sql and your Ent schema:

atlas.hcl

data "composite_schema" "app" {
  # Load first custom types first.
  schema "public" {
    url = "file://schema.sql"
  }
  # Second, load the Ent schema.
  schema "public" {
    url = "ent://ent/schema"
  }
}
env "local" {
  src = data.composite_schema.app.url
  dev = "docker://postgres/15/dev?search_path=public"
}

Usage

After setting up our composite schema, we can get its representation using the atlas schema inspect command, generate schema migrations for it, apply them to a database, and more. Below are a few commands to get you started with Atlas:

Inspect the Schema

The atlas schema inspect command is commonly used to inspect databases. However, we can also use it to inspect our composite_schema and print the SQL representation of it:

atlas schema inspect \
  --env local \
  --url env://src \
  --format '{{ sql . }}'

The command above prints the following SQL. Note, the status enum type is defined in the schema before its usage in the users.status column:

-- Create enum type "status"
CREATE TYPE "status" AS ENUM ('active', 'inactive', 'pending');
-- Create "users" table
CREATE TABLE "users" ("id" bigint NOT NULL GENERATED BY DEFAULT AS IDENTITY, "status" "status" NOT NULL, PRIMARY KEY ("id"));

Generate Migrations For the Schema

To generate a migration for the schema, run the following command:

atlas migrate diff \
  --env local

Note that a new migration file is created with the following content:

migrations/20240712090543.sql

-- Create enum type "status"
CREATE TYPE "status" AS ENUM ('active', 'inactive', 'pending');
-- Create "users" table
CREATE TABLE "users" ("id" bigint NOT NULL GENERATED BY DEFAULT AS IDENTITY, "status" "status" NOT NULL, PRIMARY KEY ("id"));

Apply the Migrations

To apply the migration generated above to a database, run the following command:

atlas migrate apply \
  --env local \
  --url "postgres://postgres:pass@localhost:5432/database?search_path=public&sslmode=disable"

Apply the Schema Directly on the Database

Sometimes, there is a need to apply the schema directly to the database without generating a migration file. For example, when experimenting with schema changes, spinning up a database for testing, etc. In such cases, you can use the command below to apply the schema directly to the database:

atlas schema apply \
  --env local \
  --url "postgres://postgres:pass@localhost:5432/database?search_path=public&sslmode=disable"

Or, using the Atlas Go SDK:

ac, err := atlasexec.NewClient(".", "atlas")
if err != nil {
    log.Fatalf("failed to initialize client: %w", err)
}
// Automatically update the database with the desired schema.
// Another option, is to use 'migrate apply' or 'schema apply' manually.
if _, err := ac.SchemaApply(ctx, &atlasexec.SchemaApplyParams{
    Env: "local",
    URL: "postgres://postgres:pass@localhost:5432/database?search_path=public&sslmode=disable",
}); err != nil {
    log.Fatalf("failed to apply schema changes: %w", err)
}

The code for this guide can be found in GitHub.

Enum Types